Current systems for speech communication generally support different operating modes for different speech applications: one mode optimized for voice recognition (VR) and another one optimized for hands-free telephony (HF). Some recent speech communication systems also support in-car communication (ICC) where speech signals are reinforced within the car passenger compartment. However, even if there are multiple microphones and loudspeakers to support several persons, current state-of-the-art systems only operate in one mode at a time.
In vehicular multi-channel speech communication systems, multiple speakers can be supported, for example, by seat-dedicated microphones, microphone arrays and/or multiple loudspeakers within the vehicle. In HF telephone mode, several passengers in the vehicle may take part in a conference call where enhancement of the speech signals for the different speakers may improve the signal quality. And an adaptive mixer may only pass the audio signal of the currently active speaker through to the far-end listener. In VR mode, only one speaker (e.g., the driver) normally is supposed to operate the system by voice, whereas other persons are considered as interfering speakers. Here again, the speech signal can also be selectively extracted by multi-channel processing. The operating mode for ICC has to make sure that the persons in the car (or room) can understand among themselves. So, for instance, the speech of the driver or front passenger may be captured by some microphones located in the front of the vehicle and played back on rear loudspeakers for the back-seat passengers.